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<h1>
API dei Componenti
</h1>
<div class="subHeader"></div>
<h2><a class="anchor" name="react.component"></a>React.Component <a class="hash-link" href="#react.component">#</a></h2>
<p>Istanze di un React Component sono create internamente a React durante il rendering. Queste istanze sono riutilizzate in rendering successivi, e possono essere accedute dai metodi del tuo componente come <code>this</code>. L&#39;unica maniera di ottenere un riferimento a una istanza di un React Component fuori da React è conservare il valore restituito da <code>ReactDOM.render</code>. All&#39;interno di altri Component, puoi utilizzare <a href="/react/docs/more-about-refs.html">i ref</a> per ottenere il medesimo risultato.</p>
<h3><a class="anchor" name="setstate"></a>setState <a class="hash-link" href="#setstate">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="k">void</span> <span class="nx">setState</span><span class="p">(</span>
<span class="kd">function</span><span class="o">|</span><span class="nx">object</span> <span class="nx">nextState</span><span class="p">,</span>
<span class="p">[</span><span class="kd">function</span> <span class="nx">callback</span><span class="p">]</span>
<span class="p">)</span>
</code></pre></div>
<p>Effettua una combinazione di <code>nextState</code> nello stato attuale. Questo è il metodo principale che va usato per scatenare aggiornamenti della UI da gestori di eventi e callback di richieste al server.</p>
<p>Il primo argomento può essere un oggetto (contenente zero o più chiavi da aggiornare) o una funzione (con argomenti <code>state</code> e <code>props</code>) che restituisce un oggetto contenente chiavi da aggiornare.</p>
<p>Ecco come utilizzarla passando un oggetto:</p>
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">setState</span><span class="p">({</span><span class="nx">mykey</span><span class="o">:</span> <span class="s1">&#39;my new value&#39;</span><span class="p">});</span>
</code></pre></div>
<p>È anche possibile passare una funzione con la firma <code>function(state, props)</code>. Questo può essere utile in certi casi quando desideri accodare un aggiornamento atomico che consulta i valori precedenti di state+props prima di impostare i nuovi valori. Ad esempio, supponi che vogliamo incrementare un valore nello stato:</p>
<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="nx">setState</span><span class="p">(</span><span class="kd">function</span><span class="p">(</span><span class="nx">previousState</span><span class="p">,</span> <span class="nx">currentProps</span><span class="p">)</span> <span class="p">{</span>
<span class="k">return</span> <span class="p">{</span><span class="nx">myInteger</span><span class="o">:</span> <span class="nx">previousState</span><span class="p">.</span><span class="nx">myInteger</span> <span class="o">+</span> <span class="mi">1</span><span class="p">};</span>
<span class="p">});</span>
</code></pre></div>
<p>Il secondo parametro (opzionale) è una funzione callback che verrà eseguita quando <code>setState</code> ha terminato e il rendering del componente è stato effettuato.</p>
<blockquote>
<p>Note:</p>
<p><em>MAI</em> modificare <code>this.state</code> direttamente, in quanto chiamare <code>setState()</code> successivamente potrebbe sovrascrivere la modifica fatta. Tratta <code>this.state</code> come se fosse immutabile.</p>
<p><code>setState()</code> non cambia immediatamente <code>this.state</code>, ma crea una transizione di stato in corso. Accedere <code>this.state</code> subito dopo aver chiamato questo metodo potrebbe potenzialmente restituire il valore precedente.</p>
<p>Non viene garantita alcuna sincronicità per le chiamate di <code>setState</code>, e le chiamate stesse potrebbero essere raggruppate per migliorare le prestazioni.</p>
<p><code>setState()</code> scatena sempre un ri-rendering a meno che la logica di rendering condizionale venga implementata in <code>shouldComponentUpdate()</code>. Se oggetti mutabili sono usati e la logica non può essere implementata in <code>shouldComponentUpdate()</code>, chiamare <code>setState()</code> solo quando il nuovo stato differisce dal precedente eviterà ri-rendering superflui.</p>
</blockquote>
<h3><a class="anchor" name="replacestate"></a>replaceState <a class="hash-link" href="#replacestate">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="k">void</span> <span class="nx">replaceState</span><span class="p">(</span>
<span class="nx">object</span> <span class="nx">nextState</span><span class="p">,</span>
<span class="p">[</span><span class="kd">function</span> <span class="nx">callback</span><span class="p">]</span>
<span class="p">)</span>
</code></pre></div>
<p>Come <code>setState()</code>, ma elimina ogni chiave preesistente che non si trova in <code>nextState</code>.</p>
<blockquote>
<p>Nota:</p>
<p>Questo metodo non è disponibile il componenti <code>class</code> ES6 che estendono <code>React.Component</code>. Potrebbe essere eliminato del tutto in una versione futura di React.</p>
</blockquote>
<h3><a class="anchor" name="forceupdate"></a>forceUpdate <a class="hash-link" href="#forceupdate">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="k">void</span> <span class="nx">forceUpdate</span><span class="p">(</span>
<span class="p">[</span><span class="kd">function</span> <span class="nx">callback</span><span class="p">]</span>
<span class="p">)</span>
</code></pre></div>
<p>In modo predefinito, quando lo stato o le proprietà del tuo componente cambiano, ne verrà effettuato il ri-rendering. Tuttavia, se questi cambiano implicitamente (ad es.: dati profondi all&#39;interno di un oggetto cambiano senza che l&#39;oggetto stesso cambi) o se il tuo metodo <code>render()</code> dipende da altri dati, puoi istruire React perché riesegua <code>render()</code> chiamando <code>forceUpdate()</code>.</p>
<p>Chiamare <code>forceUpdate()</code> causerà la chiamata di <code>render()</code> sul componente, saltando l&#39;esecuzione di <code>shouldComponentUpdate()</code>. Questo scatenerà i normali metodi del ciclo di vita per i componenti figli, incluso il metodo <code>shouldComponentUpdate()</code> di ciascun figlio. React tuttavia aggiornerà il DOM soltanto se il markup effettivamente cambia.</p>
<p>Normalmente dovresti cercare di evitare l&#39;uso di <code>forceUpdate()</code> e leggere soltanto <code>this.props</code> e <code>this.state</code> all&#39;interno di <code>render()</code>. Ciò rende il tuo componente &quot;puro&quot; e la tua applicazione molto più semplice ed efficiente.</p>
<h3><a class="anchor" name="ismounted"></a>isMounted <a class="hash-link" href="#ismounted">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kr">boolean</span> <span class="nx">isMounted</span><span class="p">()</span>
</code></pre></div>
<p><code>isMounted()</code> restituisce <code>true</code> se il rendering del componente è stato effettuato nel DOM, <code>false</code> altrimenti. Puoi usare questo metodo come guardia per chiamate asincrone a <code>setState()</code> o <code>forceUpdate()</code>.</p>
<blockquote>
<p>Nota:</p>
<p>Questo metodo non è disponibile il componenti <code>class</code> ES6 che estendono <code>React.Component</code>. Potrebbe essere eliminato del tutto in una versione futura di React.</p>
</blockquote>
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